Many existing commutators, high-speed rotary switches typically used with electric motors, comprise multiple copper segments arranged into a cylinder and anchored into a non-conducting (often phenolic) molding compound. Each segment is physically separated and electrically isolated from those adjacent to it, so that an electrical brush passing along the outer diameter of the cylinder will form a conductive path only with the segment (or segments) in contact with it at any given instant. The commutators additionally permit ends of an armature to be connected thereto.
U.S. Pat. Nos. 4,638,202 and 4,890,377 to Ebner (collectively the “Ebner patents”), incorporated herein in their entireties by this reference, illustrate and disclose examples of so-called “riser”-style commutators. As noted in the Ebner patents, a “disk-like riser plate is molded at one end of the commutator with slots for receiving and holding the coil ends of an appropriate motor armature in engagement with respective ones of the commutator segments.” Such slots are positioned intermediate protrusions designated as “risers.”
Described in the Ebner patents are conventional methods of manufacturing riser commutators. According to the patents:                In somewhat larger commutator assemblies, each commutator segment is individually formed as a bar-like element. A composite riser means is formed at one end of the commutator, including a riser portion for each commutator bar . . . . The risers are formed by machining down the commutator bars to form radially extending flanges at one end of the commutator . . . .        
Also detailed in the Ebner patents is an alternate method of manufacturing riser commutators. As noted therein:                The riser means . . . is fabricated in the form of a molded disk-like plate at the end of the commutator facing the motor. The plate is thereby separate or independent of [the] commutator segments. The riser plate is molded with locating or anchoring means in the form of a plurality of peripheral slots for receiving and holding the coil ends of the motor armature.(Numerals omitted.) According to the Ebner patents, the riser plate may be molded either as an integral part of an insulating core of a commutator or to the core and segments.        
Yet another commutator-forming method currently in use involves cold-forming a copper rod into a ring and then forcing a portion of the rod to extrude into an elongated shape. Various faces of this preform must then be ground and the preform slotted to provide appropriate electrical isolation. Phenolic insulating material is thereafter molded to the preform to form the insulating core of the resulting commutator and the ring punched to form alternating slots and risers.
Numerous difficulties exist in forming riser-style commutators in this manner. Because of tooling limitations, for example, bars or segments of these commutators often lack effective anchoring, contributing to earlier-than-desirable failure of the structures. Inability to provide anchoring into the riser heads of the commutators for the bars likewise may contribute to structural failures when commutators are made in this fashion.